Many measurement instruments need to sample and convert an analog input signal into a digital form before further processing can be performed. Examples of measurement instruments include, but are not limited to: oscilloscopes, network analyzers, spectrum analyzers, signal analyzers, protocol analyzers, printed circuit board testers, atomic force microscopes, frequency counters, time-domain reflectometers, mass spectrometers, liquid or gas chromatographs, power analyzers, data acquisition cards, ultrasonagraphs, optical distributed temperature sensing systems, polarization analyzers, digital communications analyzers, and jitter analyzers. The conversion from analog to digital form is typically accomplished by an analog-to-digital converter (ADC), sometimes also referred to as a “data converter”. As the speed of ADCs increase, the amount of digital data that needs to be stored into memory gets larger. Processing these large amounts of digital data also takes longer.
FIGS. 1 and 2 show block diagrams of typical prior art systems for converting analog data into digital data samples and storing the digital data. FIG. 1 shows a block diagram of a prior art system 10. An ADC 12 receives an analog input 14 and converts it into a digital data sample 16. The data sample 16 is stored in the memory 18 before being sent to a processor 20 for further processing.
FIG. 2 shows a block diagram of another prior art system 30. A parallel, pipelined ADC 32 receives an analog input signal 34 and converts it into N digital data samples 36. Memory controller 40 fans out the N data samples 36 arriving from ADC 32 into memory 38, which includes a number of parallel memories, The memory controller 40 fans out the data so that the higher speed data from the ADC 32 flows into the parallel memories of memory 38 at a slower rate. The data samples stored in memory 38 can be processed further by a parallel processor 42.
The data samples (16, 36) in the systems of FIGS. 1 and 2 need to be stored into the sample memory (18, 38) before processing can begin on those data samples. The speed at which the data samples (18, 38) are processed is also limited by the speed with which the processor (20, 42) can access the sample memory (18, 38). Furthermore, there is a “dead time” associated with these systems—when the system is busy processing a set of data samples from the sample memory, it is unable acquire new data. Finally, the dead time spent processing the data samples is time that the instrument is not sampling the input. As the amount of dead time increases with the amount of data to be processed, the more likely it is that rare events occurring at the input will be missed because the instrument is too busy processing the data samples instead of sampling the input.